A pressure medium of a pressure medium supply arrangement is generally understood to mean compressed air, but is not restricted thereto. For example, a compressed air supply arrangement is used in vehicles of all types, especially to supply an air spring of a vehicle with compressed air. Air suspension systems may also include level control devices with which the distance between vehicle axle and vehicle body can be adjusted. With increasing distance between vehicle axle and vehicle body, or ground clearance, spring travel is lengthened and even relatively large road surface irregularities can be surmounted without contact with the vehicle body. It is also desirable to implement a change of ground clearance as quickly as possible, increasing the demands with regard to speed, flexibility and reliability placed on a compressed air supply arrangement. For example, a compressed air supply arrangement is operated at a pressure level from 5 to 20 bar, and in some cases more. In particular, pressure medium can be stored in a pressure medium storage container at substantially higher pressure. The pressure medium, in particular compressed air, is made available using a compressor to a charging apparatus of the pressure medium supply. In order to supply a pneumatic apparatus, the pressure medium supply is pneumatically connected to a pressure medium connection and, in order to vent to an environment, is pneumatically connected to a vent connection, a pneumatic connection being switched by means of a vent valve.
In order to increase speed and flexibility of the pressure medium supply arrangement, a charging apparatus may be designed to operate the pressure medium supply arrangement in an open, partly closed or closed mode. Such a pressure medium supply arrangement is known from DE 10 2008 034 240 A1. This arrangement makes it possible both to convey the pressure medium from a pressure medium storage container into one or more pressure medium chambers of the pneumatic apparatus by means of the second compression stage of the compressor, and to convey the pressure medium from the atmosphere to the pressure medium storage container and/or to one or more pressure medium chambers by means of the first and second compression stages of the compressor. Automatically opening non-return valves as the outlet valve to the first compression chamber and inlet valve to the second compression chamber are arranged in the flow direction of a compressor line leading from a first compressor stage to a second compressor stage. A directional control valve in the compressor line provides that the two-stage compressor delivers practically in a circle in order to save the power of the first compression stage or to reduce the power in a predetermined manner. The pressure medium from the first compression chamber can be transferred either back to the suction chamber of the first compression stage or to atmosphere.
What is needed is an efficient operating mode of a pressure medium supply arrangement that goes beyond the foregoing and that is as fast, flexible and reliable as possible. This should apply, in particular, to an operating mode of a charging apparatus in the pressure medium supply arrangement.